Electrochemical Aspects of the Inhibition of Corrosion of Metals

Most forms of corrosion are the result of electrochemical processes; therefore, the effectiveness of corrosion inhibitors is largely determined by the electrochemical potential of the metal that is to be protected. This potential, together with the pH and the electrochemical reactivity of any component added to the corrosive environment, will determine whether oxidation—reduction reactions will occur on the metal surface. If difficultly-soluble compounds form on the metal as a result of such reactions, then the metal can become passivated and the additive is potentially a corrosion inhibitor.(1,2) If, on the other hand, there is no electrochemical transformation of the additive, then the role of the potential will be to affect the free energy of adsorption of the components of the solution. The surface concentration of the adsorbate will therefore depend on the potential and, as described by the Bronsted—Polanyi—Semenov principle, on the activation energy of adsorption. In this connection, one of the fundamental concepts of electrochemistry introduced by Frumkin in 1927, the potential of zero charge of a metal E q=0, is of considerable importance.